Rotary coke drum un-heading valve

ABSTRACT

A rotary coke drum un-heading valve adapted for engagement to an extremity of a coke drum having an orifice therein. The rotary coke drum un-heading valve includes a valve body, having a passage which extends therethrough along a mass flow axis and at least two valve seats that circumscribe the passage. The passage is aligned for mass flow communication with the orifice. A rotatable flow obstructing member defines a bore therein and is rotatable within the valve body between an open position, wherein the bore is in communication with the passage permitting mass flow through the un-heading valve, and a closed position, wherein mass flow through the un-heading valve is prevented by the flow obstructing member. In one embodiment, the flow obstructing member is a gate pivotable in a plane perpendicular to the mass flow axis by a valve stem rotatable about its central axis which intersects the plane.

TECHNICAL FIELD

The present invention relates generally to a device for opening andclosing a vessel containing hazardous materials, and more particularlyan un-heading system for a coke drum and an un-heading valve for such asystem.

BACKGROUND OF THE INVENTION

Delayed coking is a process employed in petroleum refineries to recoverthe heavy residual oil by-products left over after regular refiningoperations have been completed. Such recovered distillates and coke aretypically emptied into large, vertical pressure vessels called cokedrums or coking drums. Coke drums accordingly serve as waste disposalsystems for high residual, tarry oils. Volatile fumes from the cokedrums are recycled to make useful products such as gasoline and thesolid material deposited in the coke drum is resold as coke for avariety of purposes. Delayed coking thus contributes significantly tothe gross margin of the refineries and therefore to their overallfinancial performance. As such, the efficient operation of the delayedcoking operations is vital.

Delayed coking is typically performed using pairs of coke drums, whichare alternately filled and emptied in a continuous batch operation.Filled coke drums must be emptied such that the desirable hydrocarbonby-products can be saved. This process of emptying a coke drum is oftencalled de-coking. Generally, one coke drum is filled with the refiningby-products while the other is being emptied, or de-coked. Once fullyemptied and resealed, the by-products can then be redirected to theempty drum, so that the filled drum can in turn be de-coked.

De-coking typically involves cooling the entire drum by quenching withsteam followed by water, and purging the drum of all coke built uptherein. Coke which is not loose within the drum must be forciblyremoved, usually by cutting the coke from the walls of the drum usinghigh pressure water. Often, a drilling rig on top of the drum is usedwhich directs water under high pressure into the drum to fracture thesolid coke bed so the coke can be removed for sale. In order to permitthis, the top and/or bottom heads of the drum are typically removed toprovide access to the inside of the drum and to permit the dislodgedcoke to fall from the drum into a waiting receptacle below. The removalor displacement of the top and/or bottom heads of the coke drum suchthat the built up coke therein can be removed is called un-heading orde-heading the coke drum.

The heads of such huge coke drums have, in the past, been completelyremoved with each de-coking cycle. As coke drums are typically in therange of 20-30 feet in diameter and 100 feet in height, the sheer sizeof the heads of such drums caused their removal to be a process whichwas fraught with danger, both to the operators and the surroundingequipment. Many other risks have been assumed in the past by workers whocarry out the removal of such coke drum heads during the de-cokingprocess. For example, during the loosening and removal of the bottomhead, un-drained water (which has become heated during the quenchingprocess) and chunks of loose coke can fall onto workers below. Workersalso run the risk of being exposed to hazardous materials and fumes fromthe drum when the heads are opened.

As such, attempts have been made to devise automated un-heading systemswhich can be remotely operated to remove at least the bottom head of acoke drum, thereby limiting the risks assumed by workers during thede-coking operation. For example, U.S. Pat. No. 4,960,358 issued toDiGiacomo et al. on Oct. 2, 1990 discloses a bottom un-heading devicefor coke drums which includes a heat unit removably connected to a lowerend of the coke drum by swing bolts which can be disconnected byremotely operated de-tensioning equipment. Thus, the fastening mechanismbetween the bottom head and the drum can be remotely disconnected suchthat the cover unit can be completely removed from the drum by adisplaceable platform device. U.S. Pat. No. 5,785,843 issued to Antalffyet al. on Jul. 28, 1998 also discloses a coke drum de-heading device,wherein the coke drum head is hinged from the drum body by a compoundjoint which reduces the amount of headroom required to swing thedisengaged head away from the drum. An actuator is used to remotely movethe hinging head between open and closed positions.

However, while systems such as those described above are remotelyoperable to minimize the risks to human operators, any procedure whichrequires the coke drum head to be disengaged from the drum, whether byhinged operation or otherwise, remains dangerous. The complex nature ofsuch mechanisms and the size and weight of the coke drum heads theydisplace, nevertheless leave open the possibility of catastrophicconsequences should the mechanism or a part thereof fail. As such, morerecent attempts to simplify the de-heading process and make it moreefficient and safe have been made

U.S. Pat. No. 6,565,714 issued to Lah on May 20, 2003 addresses exactlythis problem, by providing a coke drum de-heading system which comprisesa rising stem, horizontally positioned de-header gate valve. Thede-header valve comprises a linear sliding blind, displaceable in aby-directional manner within the de-header valve between opposed staticand live loaded valve seats. Thus the linear sliding blind acts to openand close the bottom of the coke drum, thereby obviating the need toremove the entire bottom head. The de-header valve is coupled to thecoke drum, preferably the bottom thereof. Thus, actuation of thelinearly sliding blind of the valve from a closed position to an openposition de-heads the coke drum.

However, deficiencies exist with the linear gate de-header valve designdisclosed by Lah. Particularly, the linear motion of the stem increasesthe risk of causing leaks in the valve packing as a result of the dirtyservice encountered when positioned at the bottom of a coke drum, andthe linearly displaceable blind requires guiding during its closingstroke by guide plates and stem bushings which can also become cloggedand galled by the coke particles to which they are exposed. Anothermajor problem with the de-header valve taught by Lah is the relativelylarge amount of space which it requires around the coke drum. As thelong valve stem is horizontally displaced together with the linearlytravelling sliding blind, the overall length of the entire de-headervalve assembly could actually be greater than the diameter of the drumitself, as seen in FIG. 2 depicted by Lah, and can thereforetransversely protrude well beyond the drum support structure which canprevent access to the protruding portions of the valve Thus, althoughonly limited bottom headroom (the space available below the bottom headand the base or support substrate of the coke drum) is required, theoverall length of the sliding blind de-header valve disclosed may be along as 30 feet. This can be problematic for a number of reasons. Theprotruding end of the actuator in the de-header valve taught by Lah canoverhang the entire coke drum structure, limiting the access to parts ofthe valve. Further, while new coke drum installations could be designedto accommodate such a long and protruding bottom head valve, existingolder coke drums already in service would be difficult to retrofit withsuch large de-header valves due to relatively limited clearances aroundthe equipment.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved system for un-heading a coke drum.

It is another object of the present invention to provide an improvedcoke drum de-header valve which is compact and reliable.

Therefore, in accordance with the present invention, there is provided arotary coke drum un-heading valve adapted for engagement to an extremityof a coke drum having an orifice therein, the coke drum un-heading valvecomprising: a valve body having a passage extending therethrough along amass flow axis and at least two valve seats circumscribing said passage,said passage being aligned for mass flow communication with saidorifice; and a rotatable flow obstructing member defining a boretherein, said flow obstructing member being rotatable within said valvebody in contact with said valve seats between an open position, whereinsaid bore is in communication with said passage permitting mass flowthrough said un-heading valve, and a closed position, wherein mass flowthrough said un-heading valve is prevented by said flow obstructingmember.

There is also provided, in accordance with the present invention, a cokedrum un-heading system comprising: a coke drum having an orifice in atleast one extremity thereof; a rotary un-heading valve fastened to saidextremity in mass flow communication with said orifice and beingselectively operable to seal and open said orifice such that one of massflow into and out of said coke drum is possible; and said rotaryun-heading valve comprising a valve body having a passage extendingtherethrough along a mass flow axis and valve seats circumscribing saidpassage, said passage being in mass flow communication with saidorifice; a rotatable flow obstructing member defining a bore therein,said flow obstructing member being rotatable within said valve body incontact with said valve seats between an open position, wherein saidbore is in communication with said passage permitting mass flow throughsaid rotary un-heading valve, and a closed position, wherein mass flowthrough said rotary un-heading valve is prevented.

There is further provided, in accordance with the present invention, amethod of un-heading a coke drum having an orifice in at least oneextremity thereof, the method comprising: providing a rotary un-headingvalve fastened to said extremity in mass flow communication with saidorifice; and rotating a flow obstructing member within said rotaryun-heading valve about a pivot axis between a closed position, whereinmass flow through said rotary un-heading valve is prevented by said flowobstructing member, and an open position, wherein mass flow through saidrotary un-heading valve is permitted.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a schematic side elevation view of a coke drum having a bottomun-heading valve in accordance with the present invention;

FIG. 2 is a schematic perspective view of the coke drum bottom head andthe un-heading valve in accordance with the present invention;

FIG. 3 is a perspective view of the coke drum un-heading valve of thepresent invention;

FIG. 4 is a top plan view of the coke drum un-heading valve of FIG. 3;

FIG. 5 is a cross-sectional view taken through line 5-5 of FIG. 4;

FIG. 6 is a side elevation view of an un-heading valve of FIG. 3;

FIG. 7 is a cross-sectional view taken through line B-B of FIG. 6,showing the valve fully open;

FIG. 8 is a cross-sectional view taken through line B-B of FIG. 6,showing the valve fully closed;

FIG. 9 is a cross-sectional view taken through line B-B of FIG. 6,showing the gate partially open;

FIG. 10 is a detailed cross-sectional view of the biased valve seat,taken from detail C of FIG. 5;

FIG. 11 is a top perspective view of a coke drum un-heading valve inaccordance with an alternate embodiment of the present invention,showing the valve fully open; and

FIG. 12 is a top perspective view of a coke drum un-heading valve inaccordance with another alternate embodiment of the present invention,showing the valve fully closed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As schematically shown in FIG. 1, a vertically oriented pressure vessel,such as a coke drum 12 as employed in the delayed coking process of apetroleum refinery, is supported by an adjacent support structure 11mounted on a lower platform 13 below the coke drum 12. Such delayedcoking drums typically have a diameter between about 20 and 30 feet andstand about 75 to 100 feet tall. The lower portion 14 of the coke drum12 may have a conical shape and terminates in a lower flange 16 whichmay be in the range of 5 to 10 feet in diameter and which defines abottom orifice of the coke drum 12 through which the contents of thedrum may be evacuated during the decoking cycle. A coke drum un-headingvalve 20 is fastened to said lower flange 16 in fluid flow communicationwith the orifice defined in the base of the coke drum. The un-headingvalve 20 is selectively operable to seal the orifice while the coke drumis being filled and open the drum orifice such that mass flow out of thecoke drum and through the exit chute 18 is permitted during the decokingcycle of the coke drum. The un-heading valve 20 is opened and closed byan actuating system 22.

Referring now to FIG. 2, the coke drum de-heading system is shown ingreater detail, wherein the lower flange 16 at the base of the conicallower portion 14 of the coke drum 12 is matingly fastened to theun-heading valve 20 disposed in line between the lower flange 16 of thecoke drum and the mass flow exit chute 18 which extends through thelower platform 13 to expel contents of the drum into a receptacle (notshown) positioned beneath the chute. The un-heading valve 20, which willbe described in greater detail below, is positioned in line and in massflow communication with the orifice defined within the lower drum flange16 such that opening and closing of the un-heading valve, respectivelyopens and seals the bottom head of the coke drum. Thus, with the valvein an open position, mass flow through the valve from the inside of thecoke drum 12 to the exit chute 18 is permitted such that decoking of thecoke drum is possible. With the valve in a closed position, the bottomhead of the coke drum is sealed such that refilling of the coke dram bythe delayed coking by-products of the refining process is enabled.Although described here with reference to the bottom of the coke drum,it is understood that the un-heading valve 20 may also be disposed atthe top of the coke drum in communication with a top orifice definedtherein.

The un-heading valve 20 is a rotary valve which provides dead endisolation for the bottom and/or top orifices in a coke drum. The rotaryun-heading valve of the present invention can be any type of rotaryvalve in which the flow obstructing member travels in a rotary orpivoting motion between the open and closed positions. For instance, therotary un-heading valve of the present invention may be a rotary gatevalve, a ball valve or a butterfly valve for example, which is adaptableto the severe service conditions of the delayed coking environment. In apreferred embodiment described below, the rotary un-heading valve is arotary gate valve, pivotable in a plane substantially perpendicular tothe direction of mass flow by a valve stem which is preferably parallelto the direction of mass flow. However, it is to be understood that therotary un-heading valve can also be another type of rotary valve asdefined above.

In the preferred embodiment of the rotary un-heading valve 20, rotationof the valve stem 50 about a central axis 30 thereof enables pivoting ofthe flow obstructing member, in this case a rotatable gate 44, within aplane which is substantially transverse to a direction of mass flow 32through the valve body, between open and closed positions. Although thecentral axis 30 at least intersects the plane, it is preferablyperpendicular thereto. The actuating system 22 employed to rotate thevalve stem 50 preferably comprises an elongated torque arm 26 to whichthe valve stem 50 is engaged at a center thereof such that a portion ofthe torque arm protrudes outwardly from the valve stem, preferablysubstantially perpendicular thereto. Thus, rotation of the torque arm 26about the axis 30 causes the necessary rotation of the valve stem indirection 34. Preferably, both opposed ends of the torque arm 26 arepivotably linked to a translating end of a linear actuator 24 used topush and pull in opposite direction from each other to rotate the torquearm about the central axis 30. Although only a single linear actuator 24is necessary to rotate the torque arm, and therefore the valve stem, toopen and close the gate of the un-heading valve, two such actuators 24may be provided to ensure a redundancy such that failsafe operation ofthe actuating system 22 to open and close the un-heading valve 20 isensured. Further, the actuating system comprises a computerized controlsystem having at least a microprocessor programmed with logic whichensure a safe operation of the valve.

Referring to FIGS. 3 and 4, the rotary un-heading valve 20 comprisesgenerally an outer valve body 36, which in the embodiment shown includesfirst and second portions 36 and 39 joined together at a bolted flange41. The first portion 38 of the outer valve body 36 comprises upper andlower spaced apart walls 40 and 42 between which a substantially flatgate 44 is received for displacement within the outer valve body. Theupper and lower walls 40 and 42 define corresponding and concentricapertures 45 therein to create a passage 46 extending through the valvebody 36. Flanges 48 circumscribe the apertures 45 on each of the upperand lower walls 40 and 42, and are respectively fastenable to the lowerflange 16 of the coke drum 12 and the coke chute 18. The gate 44 definesa bore 48 therein which may be selectively aligned with the apertures 45of the upper and lower walls of the valve body to permit mass flowthrough the valve passage 46 along a mass flow axis 49, as will bedescribed in greater detail below. Particularly, the gate is rotatablebetween open and closed positions in a plane substantially perpendicularto the mass flow axis 49 by a valve stem 50, itself rotatable about itsown longitudinal axis 52 which is substantially parallel to the massflow axis 49, and therefore also substantially perpendicular to theplane within which the gate 44 is rotated.

As seen in FIG. 5, the gate 44 is rotated by the valve stem 50, withinthe substantially horizontal plane 56, between open and closed positionsof the valve. The valve stem 50 is rotatable about its longitudinal axis52 which is substantially parallel to the mass flow axis 49 andperpendicular to the plane 56. Thus the bore 48 defined within the gate44 can be selectively aligned with the apertures 45 in the upper andlower walls 40 and 42 of the outer valve body 36 to open or close thepassage through the valve. Upper and lower valve seats 58 and 60 arepositioned within the valve outer body circumscribing the apertures 45therein, and respectively mate with the upper surface 62 and lowersurface 64 of the gate 44. The valve seats 58 and 60 accordingly providea sealing contact with the gate which pivots and is guided therebetweenon at least guiding surfaces of the valve seats. Particularly, the gateis self-aligned between the opposed valve seats at all times andthroughout the opening and closing strokes of the gate. This becomesespecially useful under differential thermal expansion, for example whenthe hot contents of the coke drum first hits the relatively coolervalve. As the valve seats 58,60 maintain contact with the pivoting gate44 throughout its rotary stroke and the gate is self-aligning relativeto the valve stem, the valve seats alone guide the gate as it is pivotedbetween open and closed positions. Accordingly, no additional guidingstructure is required. In contrast, the gates of a rising stem lineargate valves of the prior art require additional guide plates and stembushings to guide the gate during at least the closing stroke thereof.These additional components increase the risk of becoming caked withcoke, which can cause damage to the valve seats and the additional guidecomponents, eventually leading to leaking during service. Particularly,the significant linear movement through the packing of the rising stemof prior art linear gate valves, greatly increases the risk of leakingduring the severe and dirty service to which they are exposed whenemployed in a coke drum un-heading valve. If coke particles get into theguide components of the linear gate valves, the gate position can changeresulting in unloading of a valve seat and accordingly leakage throughthe valve. Additionally, the rotary motion of the gate 44 minimizesmovement in the packing box of the valve body, thus enabling a superiorstem seal and reducing the possibility of packing leaks.

At least the upper valve seat 58 is biased against the upper surface 62of the gate 44 by a biasing device, such as bellows, Belleville washers,a graphite stack and/or wave springs. In the depicted embodiment, thebiasing device comprises bellows 66 which make the upper valve seat 58 alive-loaded seat which exerts a constant load force on the upper surface62 of the gate 44. Thus, extremely minimal tolerances can be maintainedbetween the surfaces of the gate and the upper and lower valve seatsthroughout the entire stroke of the rotatable gate 44 within the plane56. Preferably, the biasing device does not require any externaladjustments once installed in place between the upper valve seat and theupper wall 40 of the first portion 38 of the valve outer body.Accordingly, no additional seat force adjustments, such as external seatforce adjusting screws, exist which can increase potential leak pathsthrough the valve. Additionally, the biasing device preferably providesa fixed predetermined load force on the upper valve seat about itsentire circumference, thus eliminating the possibility of improperadjustment causing non-uniform seat loading, which is possible withlive-loaded valve seat systems of the prior art that employ externaladjusting means about the entire circumference of the live-loaded seat.The lower valve seat 60 may be either a fixed seat, as shown in FIG. 5,or may alternately be loaded against the lower surface 64 of the gate 44by a similar biasing device. In this case, both the upper valve seat 58and the lower valve seat 60 are live-loaded to exert a constantpredetermined load on the opposed surfaces 62,64 of the gate 44.

In order to ensure pressure boundary integrity within the un-headingvalve 20, as in all gate valves, an effective working seal must existbetween the moving valve stem and the valve body. Thus, the stem seal isa very important element to ensure complete pressure containment and isalso often the most common site for fluid leakage through a valvebecause this a dynamic seal. The rotary motion of the valve stem 50permits a greatly improved packing integrity which reduces thepossibility of leaks through the valve stem packing in comparison torising stems of linear gate valves of the prior art, where packingleaking about the stem is common for valves in dirty service.Particularly, such rising valve stems of the prior art typically employa single packing box wherein the stem must be retained from blowing out.

The packing of the valve stem 50 which extends completely through theun-heading valve 20 comprises a double packing box 70, having upper andlower valve stem packing 72 and 74 which seal the valve stem 50 oneither side of the gate 44. This permits the pressure acting on the stemto be equalized at both upper and lower sealing points, ensuring that,together with the fact that the valve stem 50 is substantiallyperpendicular to the gate 44, the valve stem is blowout proof. Thus, noadditional need for anti-blowout shoulders on the stem and/or thrustwashers, which are typically employed in prior art rising stemun-heading gate valves. The design of the double packing box 70 alsoensures that the stem is axially self aligned, allowing the gate to beitself axially self aligned between the opposed valve seats. Outer stemgasket seals 76 are provided about the valve stem, and are preferablyspiral wound gasket inserts which provide improved sealing overtraditional packing ring-style seals. In addition to a standard packingarrangement, the packing chamber relies on a steam purge sealingarrangement which allows for steam block to ensure a superior seal inthe upper packing chamber. The upper packing chamber is of modulardesign which simplifies maintenance.

The gate 44 is engaged to the valve stem 50 by valve stem keys 68, whichfit within corresponding keyway slots in both the valve stem and thegate. The gate 44 is therefore rotatable within the plane 56 by acorresponding rotation of the valve stem 50. The keyed engagementbetween the gate 44 and the stem 50 permits a limited amount of play inan axial direction (ie: in a direction parallel to the mass flowdirection 49). As such, the gate is axially self-aligning between theopposed valve seats at all times. This ability to self-align permits thegate to be maintained in constant contact with the valve seats, evenwhen thermal growth differentials between the two parts occur.

As seen in FIGS. 6-9, the outer valve body 36 of the un-heading valve 20is substantially half-moon shaped, and the pivotable gate valve 44 has apartially oval-shape with a curved outer edge 53 having a radius ofcurvature which substantially corresponds to that of an outer wall 55 ofthe valve body. The gate 44 accordingly has a total rotary stroke ofapproximately 70° between the fully open position, shown in FIG. 7, andthe fully closed position, shown in FIG. 8. FIG. 9 shows the gate 44partially open, particularly about 15° from the fully open position, inwhich a relatively large unsupported area of the lower valve seat 60occurs as the gate is pivoted within the valve outer body by therotatable valve stem 50. When moving between the open and closedpositions, the leading edges of the gate 44, which are in tighttolerance abutment with the valve seats, provide a scraping action whichtends to remove any coke build-up on the valve seats. Similarly, thevalve seats remove any coke build up on the flat surfaces of the gate.To improve the service life and valve effectiveness, the gate 44 mayalso be hardness treated using an air-cooled spray, such as for example,HVOF2, hard chrome plating and/or nitriding.

Referring now to FIG. 10 showing the live-loaded upper valve seat 58 ingreater detail, the biasing device 66 is permanently loaded at one endto a portion of the valve body 36 and at an opposed end to the uppervalve seat 58. Thus the valve seat 58 is constantly biased in fixed loadcontact with the upper surface 62 of the pivotable gate 44 throughoutits entire stroke within plane 56. The constant dynamic load provides aseal through a range of fluctuating temperatures and ensures that thescraper edged valve seat maintains the blind/gate free of coke build-up.

Referring to FIG. 11, the rotary coke drum un-heading valve 120 isoperated by an actuating system 122 mounted directly on the outer valvebody 36. The actuating system 122 includes actuators 24, each having oneend thereof fixed to the outer valve body by mounting brackets 137. Theactuators 24 are disposed in a common plane and orientated at an anglerelative to each other, generally defining a V-shaped configuration.Each actuator has a longitudinal axis, which intersect one another at apoint remote from the valve. The movable ends 35 of the actuators areaccordingly linearly displaceable along their respective longitudinalaxes, in opposed movement to each other. Thus, as one actuator retracts,the other extends a corresponding distance and at a corresponding rate.The moveable ends 35 of the actuators are pivotably engaged at opposedends of the torque arm linkage 126, which is fixed to the valve stem 50at a point between the opposed ends of the torque arm linkage. Thus, theactuators act to rotate the torque arm linkage 126 about the valve stem128, causing the gate 44 of the valve to open and close. Although bothactuators can be driven simultaneously to exert the most torque on thetorque arm linkage 26, as noted above one of the two actuators alone iscapable of operating the valve.

In FIG. 12, another configuration of the actuating system is provided.Particularly, the rotary un-heading valve 220 includes an actuatingsystem 222, also having two actuators 24 which are mounted to the outervalve body 36 by mounting brackets 237. However, the actuators 24 of theactuating system 222 are substantially linearly aligned, such that theirlongitudinal axes are near co-linear. In this configuration, theactuators 24 act to push and pull in opposed relation to each other inorder to pivot the torque arm linkage 226 between open and closedpositions thereof, thereby opening and closing the gate. The torque armlinkage 226 therefore has a first end fixed to the valve stem 50 and anopposed second end pivotably connected to the movable ends 35 of theactuators 24.

The rotary un-heading valves 20,120,220 provide a generally compactoverall footprint in comparison with the significantly larger risingstem linear gate valves of the prior art. Particularly, the un-headingvalves of the present invention preferably fit within a perimeterdefined by the outer wall of the coke drum. This allows for an easierretrofit of existing delayed coke drums, wherein space surrounding thedrum is at a premium. In many such existing delayed coke drums, thelimited space available proves often too small to permit a relativelylarge and cumbersome un-heading gate valve to be installed onto the cokedrum as a retrofit operation. In addition to its more compact nature,the rotary un-heading valves 20,120,220 provide, due generally to therotary movement of the flow obstructing member, improved sealing andreliability. These become vital factors for severe service uses such asdelayed coking or nuclear applications, for example.

The embodiments of the invention described above are intended to beexemplary. Those skilled in the art will therefore appreciate that theforgoing description is illustrative only, and that various alternativesand modifications can be devised without departing from the spirit ofthe present invention. Accordingly, the present is intended to embraceall such alternatives, modifications and variances which fall within thescope of the appended claims.

1. A rotary coke drum un-heading valve adapted for engagement to anextremity of a coke drum having an orifice therein, the coke drumun-heading valve comprising: a valve body having a passage extendingtherethrough along a mass flow axis and at least two valve seatscircumscribing said passage, said passage being aligned for mass flowcommunication with said orifice; and a rotatable flow obstructing memberdefining a bore therein, said flow obstructing member being rotatablewithin said valve body in contact with said valve seats between an openposition, wherein said bore is in communication with said passagepermitting mass flow through said un-heading valve, and a closedposition, wherein mass flow through said un-heading valve is preventedby said flow obstructing member.
 2. The rotary coke drum un-headingvalve as defined in claim 1, wherein said flow obstructing member is agate.
 3. The rotary coke drum un-heading valve as defined in claim 2,wherein said gate is rotatable within said valve body in a plane.
 4. Therotary coke drum un-heading valve as defined in claim 3, wherein saidplane is substantially perpendicular to said mass flow axis.
 5. Therotary coke drum un-heading valve as defined in claim 4, wherein a valvestem is engaged to said gate, said valve stem being rotatable about acentral axis thereof which intersects said plane.
 6. The rotary cokedrum un-heading valve as defined in claim 1, wherein said valve seatsprovide guiding surfaces thereon for guiding said flow obstructingmember during opening and closing strokes thereof.
 7. The rotary cokedrum un-heading valve as defined in claim 5, wherein said central axisis substantially parallel to said mass flow axis and substantiallyperpendicular to said plane.
 8. The rotary coke drum un-heading valve asdefined in claim 1, wherein at least one of said valve seats is biasedagainst said flow obstructing member by a biasing device.
 9. The rotarycoke drum un-heading valve as defined in claim 8, wherein said biasingdevice provides a load force which is constant about said at least onevalve seat.
 10. The rotary coke drum un-heading valve as defined inclaim 9, wherein said biasing device has fixed spring properties whichdefine said load force.
 11. The rotary coke drum un-heading valve asdefined in claim 9, wherein said biasing device includes at least one ofbellows, springs, Belleville washers and graphite stacks.
 12. The rotarycoke drum un-heading valve as defined in claim 5, wherein a doublepacking box seals said valve stem with said valve body, said doublepacking box having packing seals about said valve stem on opposed sidesof said gate.
 13. The rotary coke drum un-heading valve as defined inclaim 12, wherein said double packing box includes bearings disposedabout said valve stem on opposed sides of said gate.
 14. The rotary cokedrum un-heading valve as defined in claim 1, wherein said valve bodyincludes a lower wall surface fastenable to a coke chute.
 15. The rotarycoke drum un-heading valve as defined in claim 1, wherein said flowobstructing member is hardness treated.
 16. The rotary coke drumun-heading valve as defined in claim 1, further comprising an actuatingsystem operable to rotate said flow obstructing member between said openand closed positions.
 17. The rotary coke drum un-heading valve asdefined in claim 16, wherein said actuating system is remotely actuable.18. The rotary coke drum un-heading valve as defined in claim 16,wherein said actuating system includes at least one linear actuatoroperable to rotate said flow obstructing member about a pivot axis andthereby to open and close said rotary un-heading valve.
 19. The rotarycoke drum un-heading valve as defined in claim 18, wherein saidactuating system comprises two linear actuators.
 20. The rotary cokedrum un-heading valve as defined in claim 19, wherein a torque arm isengaged with said flow obstructing member, said linear actuators beingpivotably linked to said torque arm for pivoting said torque arm aboutsaid pivot axis.
 21. The rotary coke drum un-heading valve as defined inclaim 2, wherein a total rotary stroke of said gate between said openposition and said closed position is about 70 degrees.
 22. A coke drumun-heading system comprising: a coke drum having an orifice in at leastone extremity thereof; a rotary un-heading valve fastened to saidextremity in mass flow communication with said orifice and beingselectively operable to seal and open said orifice such that one of massflow into and out of said coke drum is possible; and said rotaryun-heading valve comprising: a valve body having a passage extendingtherethrough along a mass flow axis and valve seats circumscribing saidpassage, said passage being in mass flow communication with saidorifice; a rotatable flow obstructing member defining a bore therein,said flow obstructing member being rotatable within said valve body incontact with said valve seats between an open position, wherein saidbore is in communication with said passage permitting mass flow throughsaid rotary un-heading valve, and a closed position, wherein mass flowthrough said rotary un-heading valve is prevented.
 23. The coke drumun-heading system as defined in claim 22, wherein said rotary un-headingvalve is fastened to a bottom end of said coke drum.
 24. The coke drumun-heading system as defined in claim 22, wherein a coke chute isfastened to said rotary un-heading valve in fluid flow communicationwith an exit aperture of said passage.
 25. The coke drum un-headingsystem as defined in claim 22, wherein said flow obstructing member is agate.
 26. The coke drum un-heading system as defined in claim 25,wherein said gate is rotatable within said valve body in a plane. 27.The coke drum un-heading system as defined in claim 26, wherein saidplane is substantially perpendicular to said mass flow axis.
 28. Thecoke drum un-heading system as defined in claim 27, wherein a valve stemis engaged to said gate, said valve stem being rotatable about a centralaxis thereof which intersects said plane.
 29. The coke drum un-headingsystem as defined in claim 22, wherein said valve seats have guidingsurfaces thereon for guiding said flow obstructing member during openingand closing strokes of said gate.
 30. The coke drum un-heading system asdefined in claim 29, wherein said central axis is substantially parallelto said mass flow axis and substantially perpendicular to said plane.31. The coke drum un-heading system as defined in claim 22, wherein atleast one of said valve seats is biased against said flow obstructingmember by a biasing device.
 32. The coke drum un-heading system asdefined in claim 31, wherein said biasing device provides a load forcewhich is constant about said at least one valve seat.
 33. The coke drumun-heading system as defined in claim 31, wherein said biasing devicehas fixed spring properties which define said load force.
 34. The cokedrum un-heading system as defined in claim 33, wherein said biasingdevice includes at least one of bellows, springs, Belleville washers andgraphite stacks.
 35. The coke drum un-heading system as defined in claim28, wherein a double packing box seals said valve stem with said valvebody, said double packing box having packing seals about said valve stemon opposed sides of said gate.
 36. The coke drum un-heading system asdefined in claim 35, wherein said double packing box includes bearingsdisposed about said valve stem on opposed sides of said gate.
 37. Thecoke drum un-heading system as defined in claim 22, wherein said rotaryun-heading valve is sized to fit at least within a perimeter defined byan outer wall of said coke drum.
 38. The coke drum un-heading system asdefined in claim 22, further comprising an actuating system operable torotate said flow obstructing member between said open and closedpositions.
 39. The coke drum un-heading system as defined in claim 38,wherein said actuating system is remotely actuable.
 40. The coke drumun-heading system as defined in claim 38, wherein said actuating systemincludes at least one linear actuator operable to rotate said flowobstructing member about a pivot axis and thereby top open and closesaid rotary un-heading valve.
 41. The coke drum un-heading system asdefined in claim 40, wherein said actuating system comprises two linearactuators.
 42. The coke drum un-heading system as defined in claim 40,wherein a torque arm is engaged with said flow obstructing member, saidlinear actuators being pivotably linked to said torque arm for pivotingsaid torque arm about said pivot axis.
 43. The coke drum un-headingsystem as defined in claim 25, wherein a total rotary stroke of saidgate between said open position and said closed position is about 70degrees.
 44. A method of un-heading a coke drum having an orifice in atleast one extremity thereof, the method comprising: providing a rotaryun-heading valve fastened to said extremity in mass flow communicationwith said orifice; and rotating a flow obstructing member within saidrotary un-heading valve about a pivot axis between a closed position,wherein mass flow through said rotary un-heading valve is prevented bysaid flow obstructing member, and an open position, wherein mass flowthrough said rotary un-heading valve is permitted.
 45. The method asdefined in claim 44, further comprising rotating said flow obstructingmember by rotating a valve stem engaged thereto, said valve stem havinga central longitudinal axis coaxial with said pivot axis.
 46. The methodas defined in claim 45, further comprising remotely actuating rotationof said flow obstructing member using an actuating system.